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Under many of my food storage containers of plastic, there are circles with numbers and an arrow in the middle pointing at one of the numbers. What does these symbols mean?

Could it be recycling information? Plastic type? Production date? Serial number? Suitable for a special type of food?

Here is a picture of a food storage container of plastic from IKEA:

Clock-like symbols under plastic container
(click for full size)

19

This is the date the item was manufactured. The upper dial gives the year, the middle one, the month.

The bottom indicator could be a mold identifier, and in some cases, it might be a shift indicator (although this would typically be a clock going from 1 to 3, 4, or 6 depending on how shifts are allocated rather than the example showing 0 to 5).

See e.g. this manufacturer's datasheet on mold indicators: http://www.plastixs.com/pdfs/datecodeti.pdf

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    The bottom dial could also be the mold number. Most commonly these "clock" symbols only indicate the mold used to form the part -- quality dept at the factory can then quickly track down which mold may need maintenance if faulty product is noticed. I think you're completely correct that the upper two are date-related, though. – Erica Jan 15 '15 at 12:38
  • @Erica - that is a very credible alternative explanation. I am going to update my answer this evening once I've found a good reference for this. – James McLeod Jan 15 '15 at 13:06
  • The year and month is correct as defined here cpsc.gov/en/Recalls/2012/… – Huangism Jan 15 '15 at 19:07
  • Just saw a video talking about injection molding of plastic : youtube.com/watch?v=RMjtmsr3CqA . They're mentioned right at the end, at about 8:20. – Joe Nov 24 '15 at 19:00
  • Oops, the link is dead. – Catija Jan 2 '17 at 23:38
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Top to bottom: Year, Month, Week. See D-M-E injection mold components catalog p157. If a problem turns up, the date markers will allow the investgating team to run down the batch.

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    If the third one is the week, then why are there six options? – Niall Jan 11 '17 at 12:21
  • Local law says a work week is 5 days with two days off or pay overtime. 5 days into most months is 6 weeks. – user53594 Jan 19 '17 at 22:31
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At our plastic company, the last dial is the material source identifier. We source the injection molding pellets for HDPE from different manfacturers of comparable quality to keep them hungry and to keep us from having a supply crisis. 1 = company 1's resin, 2 = company 2', etc. This way you can trace a quality issue to the date and material source. sometimes it is a shift and sometimes it is a day of the week, just depends on the company.

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